interface ComputerAverage{
   public double average (double a,double b);
}
class A implements ComputerAverage{
    public double average (double a,double b){
       double aver =  0;
       aver = (a+b)/2;
       return aver ;
    }
}
class B implements ComputerAverage{
    public double average(double a,double b){
      double  aver = 0;
      aver = Math.sqrt(a*b);
      return aver;
    }
}
public class Example6_4{
      public static void main(String args[]){
        ComputerAverage computer;
        double a = 11.23,b = 22.78;
        computer = new A();
        double result =  computer.average(a,b);
        System.out.printf("%5.2f和%5.2f的算数平均值:%5.2f\n",a,b,result);
        computer = new B();
        result = computer.average(a,b);
        System.out.printf("%5.2f和%5.2f的算数平均值:%5.2f\n",a,b,result);
     }
} 
